A bipartisan group of senators said Thursday they will stand by President Obama if he attacks Iran to stop the country’s nuclear program, even as administration officials downplayed the possibility of conflict by saying Iran has not yet decided whether to produce nuclear weapons.

Lieberman said Iran has “only two choices: Peacefully negotiate to end your nuclear weapons program or expect a military strike to disable that program.”

The Obama administration, which has not ruled out a military option, said it remains committed to using sanctions and diplomacy to persuade Iran to abandon its nuclear weapons ambitions.

Defense Secretary Leon Panetta and Director of National Intelligence James Clapper said separately on Thursday that Iran has not yet made a decision to pursue nuclear weapons.

“The intelligence does not show that they’ve made the decision to proceed with developing a nuclear weapon,” Panetta said at a House hearing.

Lt. Gen. Ronald Burgess, director of the Defense Intelligence Agency, told senators Thursday that Iran is prepared to retaliate against the United States and its allies in the Middle East if it is attacked, but is unlikely to attack if not provoked.

“Iran can close the Strait of Hormuz — at least temporarily — and may launch missiles against United States forces and our allies in the region if it is attacked,” Burgess said in testimony before the Senate Armed Services Committee.

Concern over Iran and its nuclear ambitions — and how to respond — spiked in Washington this week after Iran announced it was producing its own nuclear fuel rods and that an underground uranium enrichment plant was operational. At the same time, the Iranians sent a letter welcoming the resumption of nuclear negotiations with the five U.N. Security Council countries plus Germany.

Press secretary Jay Carney said Thursday that the White House is “reviewing” the letter from Iran but did not elaborate.

Iran was also accused of attacking Israeli diplomats this week in retaliation for the assassination of an Iranian nuclear scientist.

As tensions continue to rise, anti-war lawmakers have mobilized as well to urge the United States not to begin another Middle Eastern war. Rep. Walter Jones (R-N.C.), a staunch war opponent, and Congressional Progressive Caucus Co-Chairman Rep. Keith Ellison (D-Minn.) are circulating a letter to their colleagues that tells Obama to exhaust all diplomatic options with Iran.

“A military strike against Iran could lead to a regional war in the Middle East and attacks against U.S. interests,” they wrote.

They said a strike would compel Iran to “rapidly pursue” nuclear weapons as a deterrent.

But the senators who signed onto Thursday’s resolution argued that the threat of a strike from the U.S. military was needed to deter Iran from acquiring nuclear weapons.

Testifying about the world’s leading threats to the United States, Clapper told lawmakers that Iran is not close to abandoning its nuclear ambitions. The nation’s supreme leader would likely make that judgment call and could spur an arms race in the Middle East with Iran’s neighboring countries, he said.

Testifying before a separate Senate committee last month, Clapper warned that a 2011 plot to assassinate Saudi Arabia’s ambassador to the United States — which U.S. officials said was hatched in Iran — indicates that Iran Supreme Leader Ali Khamenei and his government are willing to launch attacks in the United States.

Officials are investigating bomb attacks in India and Thailand, as well as another failed attempt in Georgia. Israel has blamed Hezbollah and Iran. The United States has labeled Iran a key financial backer of the Hezbollah terrorist group.

One of the main concerns for U.S. officials is that Iran could share its nuclear technologies with Hezbollah if it’s allowed to fully enrich uranium.

For Israel, which has been rumored to be planning its own potential strike against Iran, Graham said the sanctions have shown that the United States is committed to stopping Iran’s nuclear program.

“If anybody needed a reminder that sanctions so far haven’t stopped Iran’s nuclear program, it was the guided tour by Iran’s president of the centrifuge halls yesterday,” Netanyahu told reporters in Cyprus, according to The Associated Press. “I hope that sanctions work, but so far they haven’t worked.”

Graham said that the Senate resolution “is not an authorization to use military force,” but added that the situation in Iran must be dealt with quickly.

“To the Iranian regime, your efforts yesterday to show to the world how far you’ve gone, and how capable you are, is not going to deter us from saying no to your ambitions,” he said.